The present invention relates to a press roll and, more particularly, to a.
A press roll which comprises a flexible rotating mantle of a liquid-impervious blanket material, two disc-shaped roll heads and a clamp element with a locking element for engaging the lateral rims of the endless-loop blanket to the respective roll heads. In addition to the above-mentioned components, a press roll according to the invention includes at least one rigidly mounted nonrotating roll support beam that extends axially through the interior of the endless-loop blanket and has a stub shaft mounted at its both ends, at least one press shoe resting on the roll support beam and having a concave top face, and means for compressing the concave top face of the shoe against the flexible blanket so as to form a nip zone in cooperation with the backing roll.
In as much the inner surface of the blanket must be lubricated to reduce wear of the blanket on its interior side, the gap between the blanket and the roll heads must be made liquid-tight. Without this precaution, a risk of web contamination at the press roll could arise. Hence, it is also extremely important that the lateral rims of the blanket are connected to the roll heads in a liquid-tight fashion. Moreover, it is important that this connection can be engaged and disengaged quickly, because normal wear of the blanket necessitates blanket replacement at regular intervals, whereby the time consumed in replacing the blanket should be made maximally short.
For instance in patent application U.S. Pat. No. 4,975,152 is disclosed an arrangement for engaging an endless-loop blanket in a liquid-tight sealed fashion to the press roll heads. According to the teaching of the publication, the lateral edge of the endless-loop blanket is secured to the head of the press roll by means of a hose-like inflatable annular seal element made from a flexible material. The head comprises a head body wherein the securing element is mounted, complemented with a two-part securing sector member which is pivotally mounted so as to be rotatable into a position facing the exterior side of the securing element. The interior of the securing element is pressurizable so as to expand the securing element, whereby the endless-loop blanket adapted between the securing element and the securing sector member is compressed therebetween thus establishing a liquid-tight joint. According to the teaching of the publication, the securing sector member may include barbs directed radially inwardly toward the endless-loop blanket in order to improve the clamping of the blanket. The arrangement disclosed in the publication, however, is problematic under disturbance situations in as much the pressure applied to the interior of the securing element may then fall or even disappear entirely, whereby the endless-loop blanket may detach from the heads thus causing the production to halt. Also the barbs may damage the endless-loop blanket. If a damage to the blanket occurs, the lubricating oil can soil the machinery and its surroundings in a problematic manner.
In patent publication U.S. Pat. No. 5,700,357 is disclosed an arrangement aiming to overcome the above kind of detachment of the endless-loop blanket during a disturbance situation. According to the teaching of the publication, the blanket is secured using an annular hose-like seal element filled with pressurized air in combination with an array of mechanically-driven wedged clamp segments by means of which the blanket is pressed against a circumferential clamp ring and barbs directed therefrom radially inwardly toward the rim of the blanket.
Nevertheless, the arrangements taught by patent publications U.S. Pat. No. 4,975,152 and U.S. Pat. No. 5,700,357 still remain problematic in regard to the accuracy of blanket alignment at the ends of the press roll, that is, at the roll heads. Such inaccuracies in the blanket alignment may cause uneven and unstable run of the press roll blanket and increase its wear.
In patent publication Fl 87094 is disclosed an alternative arrangement for clamping the blanket to the roll heads. Herein, the edge portion of the blanket is bent radially inward and clamped by means of a clamp ring against a seal surface of the roll head end wall. The publication also teaches that bending of the blanket edge portion is made easier by way of providing the blanket edge with a plurality of indents that thus form tongues therebetween. Each one of the tongues has in the tongue area a hole that can be aligned with a clamp element, whereby the tongue under a tensional stress will stay clamped at a given distance from the center axis of the roll. However, this kind of blanket clamping arrangement is handicapped by the large number of tongues to be clamped that makes blanket replacement a time-consuming operation. Furthermore, the blanket is subjected to an extremely high stress at the bending point of the tongues in a manner that may shorten its service life. Also the blanket clamping holes and indents are subjected to stresses that may cause damage to the blanket and induce uneven tension along the circumferential rim of the blanket.
From patent publication Fl 96525 is further known an arrangement, wherein an annularly wedged member is used for clamping the blanket by way of tensioning the blanket against a clamp surface. This kind of clamping arrangement is problematic in as much the wedged member imposes a shearing stress on the blanket material in a manner that may shorten the blanket service life. Furthermore, the blanket may crimple problematically during its replacement.
It is an object of the present invention to eliminate or at least reduce the problems hampering the above-described prior-art arrangements.
It is a further object of the present invention to provide a press roll having its endless-loop blanket clamped to the roll heads in a liquid-tight and reliable fashion. It is still another object of the present invention to provide a press roll offering a rapid and easy replacement of the endless-loop blanket. It is still a further object of the present invention to provide a press roll, wherein a malfunction of its clamp element cannot invoke a major disturbance situation due to defective clamping of the endless-loop blanket by allowing the blanket to detach from the roll heads.
In order to realize the above-mentioned goals, a press roll according to the invention is principally characterized by having between the pressurized-medium-filled clamp element and the endless-loop blanket adapted an elastic annular element that during the pressurization of the clamp element presses the blanket against the inner rim surface of the sector plates and, at the decompression or reduction of the pressure of the clamp element, keeps the clamp element under external compression. The roll head construction comprising a plurality of adjacent sector plates reduces the manufacturing cost of the roll head.
A preferred embodiment of the invention is characterized in that the sector plate incorporates one or move grooves against which the blanket is arranged to be compressively sealed/clamped to the roll head.
Another preferred embodiment of the invention is characterized in that the pressurized-medium-filled clamp element is an annular clamp means fillable with a pressurized liquid medium.
A still another preferred embodiment of the invention is characterized in that the sector plates are locked to the roll head body in the radial direction of the inner wall thereof by means of an annularly wedged tongue-and-groove joint.
A further another preferred embodiment of the invention is characterized in that the roll head includes a clamp means adapted movable in the radial direction of the roll head so as to cooperate with the endless-loop blanket for clamping the rim of the blanket to the roll head, said clamp means comprising a gearwheel rotatable from the exterior side of the roll head and a toothed locking pin cooperating with the teeth of the gearwheel so as to be movable in the radial direction of the roll head by means of said gearwheel for engaging the pin into a locking hole and disengaging the pin from said locking hole.
One of the major advantages of a press roll according to the invention is the highly reliable clamping of the blanket to the roll head. The clamp means that clamp the endless-loop blanket to the roll head retain the blanket in place also during a malfunction of the pressurized-medium-filled clamp element, whereby costly situations caused by an entirely detached blanket cannot arise. Moreover, the press roll according to the invention offers a blanket-clamping system free from sharp points causing wear of the endless-loop blanket and no unevenly distributed forces are imposed on the blanket in as much the blanket is primarily clamped by a pressurized-medium-driven clamp means, whereby the locking elements serve as securing members of blanket clamping only.
Furthermore, the press roll according to the invention offers the benefits of easy and quick replacement of the blanket. The locking elements used in the press roll according to the invention secure that the blanket will be aligned in a correct position resting in a balanced manner on both roll heads.